to the conditions which have brought about the evolution of
man from lower forms. The instances of reversion here discussed
are microcephalism, which Darwin wrongly interpreted as atavistic,
supernumerary mammae, supernumerary digits, bicornuate uterus, the
development of abnormal muscles, and so on. Brief mention is also made
of correlative variations observed in man.

Darwin next discusses the question as to the manner in which man
attained to the erect position from the state of a climbing quadruped.
Here again he puts the influence of Natural Selection in the first
rank. The immediate progenitors of man had to maintain a struggle for
existence in which success was to the more intelligent, and to those
with social instincts. The hand of these climbing ancestors, which
had little skill and served mainly for locomotion, could only undergo
further development when some early member of the Primate series came to
live more on the ground and less among trees.

A bipedal existence thus became possible, and with it the liberation
of the hand from locomotion, and the one-sided development of the human
foot. The upright position brought about correlated variations in the
bodily structure; with the free use of the hand it became possible
to manufacture weapons and to use them; and this again resulted in a
degeneration of the powerful canine teeth and the jaws, which were then
no longer necessary for defence. Above all, however, the intelligence
immediately increased, and with it skull and brain. The nakedness of
man, and the absence of a tail (rudimentariness of the tail vertebrae)
are next discussed. Darwin is inclined to attribute the nakedness of
man, not to the action of natural selection on ancestors who originally
inhabited a tropical land, but to sexual selection, which, for aesthetic
reasons, brought about the loss of the hairy covering in man, or
primarily in woman. An interesting discussion of the loss of the tail,
which, however, man shares with the anthropoid apes, some other monkeys
and lemurs, forms the conclusion of the almost superabundant material
which Darwin worked up in the second chapter. His object was to
show that some of the most distinctive human characters are in all
probability directly or indirectly due to natural selection. With
characteristic modesty he adds ("Descent of Man", page 92.): "Hence, if
I have erred in giving to natural selection great power, which I am
very far from admitting, or in